Japan is set to fire seven satellites into orbit over the coming years as part of plans to enhance GPS so locations can be pin-pointed to within centimetres rather than metres.
The Quasi-Zenith Satellite System (QZSS) project began back in 2010 with the launch of QZS-1 “Michibiki”, and engineers at contractor Mitsubishi Electric …

Re: Is this just WAAS?

Re: Is this just WAAS?

Re: Is this just WAAS?

I don't think so. I think that it's more about the fact that in Tokyo, and most cities in Japan, the horizon is about 15 degrees instead of 180 degrees in the countryside or 90 degrees in other cities. It's almost impossible to see 4 GPS satellites at the same time, let alone more.

This is more about putting satellites into very eliptical orbits (or geo), so that they are above the local horizon for longer, so you can still see enough of them to get a lock, or enough of them to have reasonable accuracy. At the same time, yes it makes sense to add differentials.

Is there a rocket scientist in the house?

Re: Is there a rocket scientist in the house?

I wondered about this.

If they're going for a geosynchronous SV, just have the one with a footprint pointing at Japan. Ahh, but then it's not at the zenith from Japan and you don't get cen-ti-meee-terr accuracy, (cos that's soooo important for your average user). I would hazard a guess that they'd need to use inclined elliptical orbits so the SV is wafting North and South of the equator on a daily basis, hence the need for 4 of them each with the inclination axis offset by 90° longitude to ensure there is an aggregated link overhead all the time. That's why they call it "Quasi-Zenith" I suppose.

Re: Is there a rocket scientist in the house?

Is it possible to maintain a geosynchronous orbit with the mass of these satellites at the altitude at which they orbit? I honestly don't know. That's the only thing I could imagine though, but I'm certainly no rocket scientist.

Re: Is there a rocket scientist in the house?

Re: Is there a rocket scientist in the house?

Looks like they're putting 4 SVs in inclined nominally-circular geosynchronous orbits. An inclined geosynch orbit, ie. not parallel to the equator, "nods" when seen from the ground - it stays with you (approximately) in longitude but goes up and down (N and S) in latitude symmetrically about 0degN.

Put more than one in similar orbits in similar longitude but different directions of the inclination and you can ensure they take turns in being "up" where you are.

BTW, AIUI real elliptical orbits give a figure-8 path seen from the ground as it leads and lags in longitude as the latitude changes. More eccentricity can make one loop of the '8' much fatter than the other, so you can almost get a straight-up-and-down apparent path for the part you're interested in - ie. over your own territory - with the larger loop happening when the SV is below the horizon from your locale. And/or make the SV spend >50% of the time in your desired half of the world (but not much greater).

Not sure, but I think India and China are also doing this sort of thing for enhanced local coverage.

Again AIUI, these are not only as a WAAS or EGNOS (sp?) but you can of course use timed signals from the extra SVs in your simultaneous equation set for finding position, so long as they send them and you have good enough ephemeris about the sat positions with time.

Re: Is there a rocket scientist in the house?

" Is it possible to maintain a geosynchronous orbit with the mass of these satellites at the altitude at which they orbit? I honestly don't know. That's the only thing I could imagine though, but I'm certainly no rocket scientist."

The military already have plenty enough accuracy to lob a hundred kilos of Semtex into a specific meter-sized location from thirty miles away (or more if we're talking nuclear warheads). Centimeter-level accuracy will make zero difference when those kilos go boom.

Civilian accuracy is the next step in allowing us personal cars that we don't have to drive, which is the next best thing to flying cars that we'll not be seeing until the portable fusion reactor can power the gravity modulation plates that nobody has invented yet.

Address confusion

If you've ever tried to find a building by its street address in Japan, you'll know why everyone has GPS on their phone.

There are no street names - instead each block has a number, and each house on that block. Except that the numbers are not sequential. With just an address it can be nigh impossible to find somewhere in an unfamiliar area, short of just wandering around and hoping.

Re: Address confusion

In a gerontocratic society with strict social hierarchies, the Japanese approach to addresses makes perfect sense.

A very similar system in the UK applies to the Law Courts, and for more or less the same reasons. The equivalent of a GPS system and satnav for the English judicial system would destroy the careers of a large number of very well paid people, which is one reason why attempts to improve the system have been so unsuccessful.

Compatible with existing GPS systems?

Re: Compatible with existing GPS systems?

I imagine not, but the manufacturers of the products for the relevant areas have now got at least 4 years to prepare, and at the present rate of technical progress nobody in Japan over the age of 50 is likely to be seen dead with a 4 year old phone.

Re: Compatible with existing GPS systems?

In theory it there is no reason why not. The new satellites just need to transmit a datastream in the same band, with satellite position data that represents the position of the satellite. It doesn't matter if the satellite is in a different orbit.

Bah!

Re: Bah!

If we have enough satellites up there serving duty as part of the global positioning network then - combined - they can be rapidly redeployed to restore coverage. When the big one hits half of them will survive, due some some giant ball of rock or other being between the sun and the satellites. Between launches of emergency reserve satellites (2-3 units per system), activation of in-flight spares (1 per system, typically in MEO over the dark side), and the ability to reposition some of the existing nodes of some of the systems full global coverage could be restored to multi-band systems in days.

Getting the various governments to cooperate enough to retask satellites for that, however, could be difficult.